Scanning optical system and scanning optical device

Abstract

There is provided a scanning optical system used with a deflection mirror that produces sinusoidal vibrations. The scanning optical system includes a first lens having a positive power, and a second lens having a negative power. In this configuration, the first lens and the second lens are arranged in this order from a deflection mirror side. Further, the scanning optical system has an arcsine property and satisfies a condition: −1.15 <f 1/ f 2<−0.70   (1) where f 1 (mm) represents a focal length of the first lens, and f 2 (mm) represents a focal length of the second lens.

1. A scanning optical system used with a deflection mirror that produces sinusoidal vibrations, comprising:
 a first lens having a positive power; and 
 a second lens having a negative power, 
 wherein: 
 the first lens and the second lens are arranged in this order from a deflection mirror side; and 
 the scanning optical system has an arcsine property and satisfies a condition:
   −1.15 <f 1 /f 2<−0.70  (1) 
 
 where f 1  (mm) represents a focal length of the first lens, and f 2  (mm) represents a focal length of the second lens. 
 
   
   
     2. The scanning optical system according to  claim 1 ,
 wherein the scanning optical system satisfies a condition: 
 
     
       
         
           
             
               
                 
                   
                     - 
                     8.00 
                   
                   < 
                   
                     
                       
                         
                           r 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         + 
                         
                           r 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       
                         
                           r 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         - 
                         
                           r 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     - 
                     
                       
                         65.6 
                         ⁢ 
                         D 
                       
                       f 
                     
                   
                   < 
                   
                     - 
                     4.00 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
       where r 1  (mm) represents a radius of curvature of a first surface of the first lens located on the deflection mirror side, r 2  (mm) represents a radius of curvature of a second surface of the first lens located oppositely to the first surface, D (mm) represents a distance from a point at which a laser beam is incident on the deflection mirror to the first surface of the first lens, and f represents a total focal length of the scanning optical system. 
     
   
   
     3. The scanning optical system according to  claim 1 ,
 wherein the scanning optical system satisfies a condition: 
 
     
       
         
           
             
               
                 
                   
                     - 
                     4.20 
                   
                   < 
                   
                     
                       
                         r 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                       + 
                       
                         r 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                     
                     
                       
                         r 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                       - 
                       
                         r 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                     
                   
                   < 
                   
                     - 
                     1.20 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
       where r 3  (mm) represents a radius of curvature of a first surface of the second lens located on the deflection mirror side, and r4 (mm) represents a radius of curvature of a second surface of the second lens located oppositely to the first surface. 
     
   
   
     4. The scanning optical system according to  claim 1 ,
 wherein the scanning optical system satisfies a condition:
   0.05 <s/f ≦0.65  (4) 
 
 where s (mm) represents a distance between two principal points of the scanning optical system, and f represents a total focal length of the scanning optical system. 
 
   
   
     5. The scanning optical system according to  claim 1 ,
 wherein at least one of surfaces of the first lens is an aspherical surface, 
 wherein the scanning optical system satisfies a condition: 
 
     
       
         
           
             
               
                 
                   
                     
                       
                         - 
                         4.7 
                       
                       ⁢ 
                       E 
                     
                     - 
                     3 
                   
                   < 
                   
                     ASP 
                     
                       f 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       × 
                       
                         tan 
                         2 
                       
                       ⁢ 
                       ω 
                       × 
                       D 
                     
                   
                   < 
                   
                     
                       1.0 
                       ⁢ 
                       E 
                     
                     - 
                     3 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
       where ASP (mm) represents a difference between SAG amounts of surfaces of the first lens, ω (degree) represents an angle of view of a laser beam incident on the first lens, and a notation E means a power of 10 with an exponent specified by a number to the right of E. 
     
   
   
     6. The scanning optical system according to  claim 1 ,
 wherein the scanning optical system satisfies a condition: 
 
     
       
         
           
             
               
                 
                   
                     - 
                     0.42 
                   
                   < 
                   
                     ASP 
                     
                       
                         arcsin 
                         2 
                       
                       ⁢ 
                       ω 
                       × 
                       D 
                     
                   
                   < 
                   0.02 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
       where ASP (mm) represents a difference between SAG amounts of surfaces of the first lens, and ω (degree) represents an angle of view of a laser beam incident on the first lens. 
     
   
   
     7. The scanning optical system according to  claim 1 , wherein the deflection mirror includes a micromirror. 
   
   
     8. A scanning optical device, comprising:
 a light source unit configured to emit a laser beam while on-off modulating the laser beam in accordance with a modulating signal generated based on image data; 
 a deflection mirror that produces sinusoidal vibrations to deflect the laser beam emitted by the light source unit; 
 a scanning optical system according to  claim 1 ; and 
 a scan target unit configured such that a scan target surface on which the laser beam deflected by the deflection mirror scans in a scanning direction is moved perpendicularly to the scanning direction. 
 
   
   
     9. The scanning optical device according to  claim 8 , wherein the deflection mirror includes a micromirror.